Intervertebral implant having features for controlling angulation thereof

ABSTRACT

An intervertebral implant includes a first plate having an inner surface, an outer surface, a ball shaped protuberance projecting from the inner surface and an annular groove surrounding the ball shaped protuberance. The implant includes a second plate having an inner surface, an outer surface, a curvate socket formed in the inner surface of the second plate and a raised rim surrounding the curvate socket. The first and second plates are assembled together so that the inner surfaces of the plates oppose one another and the ball shaped protuberance is disposed in the curvate socket and the annular groove aligned with the raised rim. The assembled first and second plates angulate and rotate relative to one another.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 10/177,378, filed Jun. 21, 2002, the disclosure of which ishereby incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates generally to a spinal implant assembly forimplantation into the intervertebral space between adjacent vertebralbones to simultaneously provide stabilization and continued flexibilityand proper anatomical motion, and more specifically to such a devicethat utilizes a spider spring force restoring element.

BACKGROUND OF THE INVENTION

The bones and connective tissue of an adult human spinal column consistsof more than 20 discrete bones coupled sequentially to one another by atri-joint complex that consists of an anterior disc and the twoposterior facet joints, the anterior discs of adjacent bones beingcushioned by cartilage spacers referred to as intervertebral discs.These more than 20 bones are anatomically categorized as being membersof one of four classifications: cervical, thoracic, lumbar, or sacral.The cervical portion of the spine, which comprises the top of the spine,up to the base of the skull, includes the first 7 vertebrae. Theintermediate 12 bones are the thoracic vertebrae, and connect to thelower spine comprising the 5 lumbar vertebrae. The base of the spine isthe sacral bones (including the coccyx). The component bones of thecervical spine are generally smaller than those of the thoracic spine,which are in turn smaller than those of the lumbar region. The sacralregion connects laterally to the pelvis. While the sacral region is anintegral part of the spine, for the purposes of fusion surgeries and forthis disclosure, the word spine shall refer only to the cervical,thoracic, and lumbar regions.

The spinal column is highly complex in that it includes these more than290 bones coupled to one another, housing and protecting criticalelements of the nervous system having innumerable peripheral nerves andcirculatory bodies in close proximity. In spite of these complications,the spine is a highly flexible structure, capable of a high degree ofcurvature and twist in nearly every direction.

Genetic or developmental irregularities, trauma, chronic stress, tumors,and degenerative wear are a few of the causes that can result in spinalpathologies for which surgical intervention may be necessary. A varietyof systems have been disclosed in the art that achieve immobilizationand/or fusion of adjacent bones by implanting artificial assemblies inor on the spinal column. The region of the back that needs to beimmobilized, as well as the individual variations in anatomy, determinethe appropriate surgical protocol and implantation assembly. Withrespect to the failure of the intervertebral disc, the interbody fusioncage has generated substantial interest because it can be implantedlaparoscopically into the anterior of the spine, thus reducing operatingroom time, patient recovery time, and scarification.

Referring now to FIGS. 6 and 7, in which a side perspective view of anintervertebral body cage and an anterior perspective view of a postimplantation spinal column are shown, respectively, a more completedescription of these devices of the prior art is herein provided. Thesecages 10 generally comprise tubular metal body 12 having an externalsurface threading 14. They are inserted transverse to the axis of thespine 16, into preformed cylindrical holes at the junction of adjacentvertebral bodies (in FIG. 7 the pair of cages 10 are inserted betweenthe fifth lumbar vertebra (L5) and the top of the sacrum (S1)). Twocages 10 are generally inserted side by side with the external threading14 tapping into the lower surface of the vertebral bone above (L5), andthe upper surface of the vertebral bone (S1) below. The cages 10 includeholes 18 through which the adjacent bones are to grow. Additionalmaterials, for example autogenous bone graft materials, may be insertedinto the hollow interior 20 of the cage 10 to incite or accelerate thegrowth of the bone into the cage. End caps (not shown) are oftenutilized to hold the bone graft material within the cage 10.

These cages of the prior art have enjoyed medical success in promotingfusion and grossly approximating proper disc height. it is, however,important to note that the fusion of the adjacent bones is an incompletesolution to the underlying pathology as it does not cure the ailment,but rather simply masks the pathology under a stabilizing bridge ofbone. This bone fusion limits the overall flexibility of the spinalcolumn and artificially constrains the normal motion of the patient.This constraint can cause collateral injury to the patient's spine asadditional stresses of motion, normally borne by the now-fused joint,are transferred onto the nearby facet joints and intervertebral discs.It would therefore, be a considerable advance in the art to provide animplant assembly which does not promote fusion, but, rather, whichnearly completely mimics the biomechanical action of the natural disccartilage, thereby permitting continued normal motion and stressdistribution.

It is, therefore, an object of the invention to provide anintervertebral spacer that stabilizes the spine without promoting a bonefusion across the intervertebral space.

It is further an object of the invention to provide an implant devicethat stabilizes the spine while still permitting normal motion.

It is further an object of the invention to provide a device forimplantation into the intervertebral space that does not promote theabnormal distribution of biomechanical stresses on the patient's spine.

It is further an object of the invention to provide an artificial discthat has a plat attachment device 9 for attaching the plates of theartificial disc to the vertebral bones between which the disc isimplanted) with superior gripping and holding strength upon initialimplantation and thereafter.

It is further an object of the invention to provide an artificial discplate attachment device that deflects during insertion of the artificialdisc between vertebral bodies.

It is further an object of the invention to provide an artificial discplate attachment device that conforms to the concave surface of avertebral body.

It is further an object of the invention to provide an artificial discplate attachment device that does not restrict the angle at which theartificial disc can be implanted.

It is further an object of the invention to provide an artificial discthat supports tension loads.

It is further an object of the invention to provide an artificial discthat provides a centroid of motion centrally located within theintervertebral space.

Other objects of the invention not explicitly stated will be set forthand will be more clearly understood in conjunction with the descriptionsof the preferred embodiments disclosed hereafter.

SUMMARY OF THE INVENTION

The preceding objects are achieved by the invention, which is anartificial intervertebral disc or intervertebral spacer devicecomprising a pair of support members (e.g., spaced apart plates), eachwith an exterior surface. Because the artificial disc is to bepositioned between the facing surfaces of adjacent vertebral bodies, theplates are arranged in a substantially parallel planar alignment (orslightly offset relative to one another in accordance with properlordotic angulation) with the exterior surfaces facing away from oneanother. The plates are to mate with the vertebral bodies so as to notrotate relative thereto, but rather to permit the spinal segments toaxially compress and bend relative to one another in manners that mimicthe natural motion of the spinal segment. This natural motion ispermitted by a the performance of a spring disposed between the securedplates, and the securing of the plates to the vertebral bone is achievedthrough the use of a vertebral body contact element including, forexample, a convex mesh attached to the exterior surface of each plate.Each convex mesh is secured at its perimeter, by laser welds, to theexterior surface of the respective plate. While domed in its initialundeflected conformation, the mesh deflects as necessary duringinsertion of the artificial disc between vertebral bodies, and, once theartificial disc is seated between the vertebral bodies, the mesh deformsas necessary under anatomical loads to reshape itself to the concavesurface of the vertebral endplate. Thus, the wire mesh is deformablyreshapable under anatomical loads such that it conformably deflectsagainst the concave surface to securably engage the vertebral bodyendplate. Stated alternatively, because the wire mesh is convexly shapedand is secured at its perimeter to the plate, the wire mesh is biasedaway from the plate but moveable toward the plate (under a loadovercoming the bias; such load is present, for example, as an anatomicalload in the intervertebral space) so that it will securely engage thevertebral body endplate when disposed in the intervertebral space. Thisaffords the plate having the mesh substantially superior gripping andholding strength upon initial implantation, as compared with otherartificial disc products. The convex mesh further provides anosteoconductive surface through which the bone may ultimately grow. Themesh preferably is comprised of titanium, but can also be formed fromother metals and/or non-metals. Inasmuch as the mesh is domed, it doesnot restrict the angle at which the artificial disc can be implanted. Itshould be understood that while the flexible dome is described hereinpreferably as a wire mesh, other meshed or solid flexible elements canalso be used, including flexible elements comprises of non-metals and/orother metals. Further, the flexibility, deflectability and/ordeformability need not be provided by a flexible material, but canadditionally or alternatively be provided mechanically or by othermeans.

To enhance the securing of the plates to the vertebral bones, each platefurther comprises at least a lateral porous ring (which may be, forexample, a sprayed deposition layer, or an adhesive applied beaded metallayer, or another suitable porous coating known in the art). This porousring permits the long-term ingrowth of vertebral bone into the plate,thus permanently securing the prosthesis within the intervertebralspace. The porous layer may extend beneath the domed mesh as well, butis more importantly applied to the lateral rim of the exterior surfaceof the plate that seats directly against the vertebral body.

The spring disposed between the plates provides a strong restoring forcewhen a compressive load is applied to the plates, and also permitsrotation and angulation of the two plates relative to one another. Whilea wide variety of embodiments are contemplated, a preferred springincludes a spider spring utilized as the restoring force providingelement. In general, a spider spring (due to its strength and structuralstability) is highly suitable for use as a restoring force providingsubassembly in an intervertebral spacer element that must endureconsiderable cyclical loading in an active human adult.

In particular, in order for the overall device to mimic the mechanicalflexibility of the natural disc, it is desirable that the spring providerestoring forces that (1) are directed outward against the opposingplates, when a compressive load is applied to the plates; (2) thatpermit lateral bending and flexion and extension bending of the platesrelative to parallel; (3) that do not permit lateral translation of theplates relative to one another during such bending; and (4) that do notsubstantially interfere with the rotation of the opposing platesrelative to one another. The spider springs disclosed herein providesuch functionality.

The spider spring of the invention has a plurality of spring armsextending radially and upwardly and/or downwardly from a central hubsuch that arm separation spaces are formed. The spring arms can beradially straight, where the height of the spider spring is linearlyrelated to the radial length of the spring arm, or the spring arms canbe radially bowed, where the height of the spider spring is not linearlyrelated to the radial length of the spring arm (but rather the spiderspring may, for example, be parabolic in shape). As a compressive loadis applied to a spider spring, the forces are directed into a hoopstress that causes the spring arms to separate and move radiallyoutwardly. This hoop stress is counterbalanced by the material strengthof the spider spring, and the strain of the material causes a deflectionin the heights of the spider spring. Stated equivalently, a spiderspring responds to a compressive load by deflecting compressively, butprovides a restoring force that is proportional to the elastic modulusof the material in a hoop stressed condition. Thus, the restoring forceof a spider spring is proportional to the elastic properties of thematerial from which it is made.

In addition, changing the configuration of the spring arms may modifythe magnitude of the compressive load support and restoring forceprovided by the spider spring. Specifically, a variety of spring armsare illustrated and discussed herein. In some embodiments, the springarms have radially parallel sides, forming radially widening armseparation spaces. In other embodiments, the spring arms have radiallyoutwardly diverging sides, forming radially parallel arm separationspaces. In other embodiments, the spring arms have radially outwardlydiverging and curving sides, forming curved arm separation spaces. Thenumber and shape of the spring arms, and the formation of the resultingarm separation spaces, can be varied to accommodate desiredapplications, inasmuch as varying the dimensions will affect thebehavior of the spider spring in expansion and retraction.

Additional configurations of the spring arms are possible, and areillustrated and discussed herein, to affect the behavior of the spiderspring in expansion and retraction. In other embodiments, each springarm is doubled, with a lower portion extending radially downwardly fromthe central hub and an upper portion extending radially upwardly fromthe central hub. It is possible to achieve a similar double spring armconfiguration by mounting a balled spider spring to a bored spiderspring to create a spring comprising opposing spider springs rotatingand angulating with respect to one another about the resultingball-and-bore joint at their narrow ends. It is also possible to achievea similar double spring arm configuration by mounting a balled spiderspring to a socketed spider spring to create a spring comprisingopposing spider springs rotating and angulating with respect to oneanother about the resulting ball-and-socket joint at their narrow ends.In other embodiments, some spring arms extend radially downwardly fromthe central hub and other spring arms extend radially upwardly from thecentral hub. Preferably in these embodiments, the upwardly extendingspring arms and the downwardly extending spring arms alternate.

Further configurations of the spring arms are possible, and areillustrated and discussed herein, to affect the behavior of the spiderspring in expansion and retraction. In some embodiments, the spring armshave at least one concentric or radial characteristic that alters theperformance of the spider spring in expansion and/or retraction. Morespecifically, in some embodiments, at least one spring arm is radiallywavy. In other embodiments, at least one spring arm is radially thinning(the portion of the arm near the central hub is thicker than the portionof the arm near the outer edge of the arm). In other embodiments, atleast one spring arm is radially thickening (the portion of the arm nearthe central hub is thinner than the portion of the arm near the outeredge of the arm). In other embodiments, at least one spring arm isconcentrically grooved, having grooves that are similarly dimensioned toone another regardless of their relative radial distance from thecentral hub, or grooves that vary in dimension from one anotherdepending on their relative radial distance from the central hub. Inother embodiments, at least one spring arm is concentrically wavy. Inother embodiments, at least one spring arm is radially grooved. In otherembodiments, at least one spring arm is concentrically bowed, with theconcave surface facing down. In other embodiments, at least one springarm is concentrically bowed, with the concave surface facing up. Itshould be noted that with regard to spring arms having radial grooves,one or both the depth and the width of each groove can be (1) decreasingalong the length of the groove from the outer edge of the spring armtoward the central hub, (2) increasing along the length of the groovefrom the outer edge of the spring arm toward the central hub, (3)uniform along the length of the groove from the outer edge of the springarm toward the central hub, or (4) varied along the length of eachgroove from the outer edge of the spring arm toward the central hub,either randomly or according to a pattern. It should be further notedthat there is no lower or upper limit on the number of groovescontemplated by the invention.

For disposing the spider spring (whichever spider spring embodiment ischosen for the clinical application) between the plates, each spiderspring embodiment has at least one feature suitable for this purpose,and the plates of the artificial disc comprise cooperating featuressuitable for this purpose. With regard to the spider spring couplingfeatures, each spider spring embodiment has at least one wide end of thespider spring that expands and retracts as described above. Some spiderspring embodiments have a solid central hub at a narrow end of thespider spring. Other spider spring embodiments have a bored central hubat a narrow end of the spider spring. Still other spider springembodiments have a ball-shaped protuberance on a narrow end of thespider spring, similar to the ball-shaped protuberance described belowwith respect to the plate embodiments. Still other spider springembodiments have a curvate socket on a narrow end of the spider spring,similar to the curvate socket described below with respect to the plateembodiments.

With regard to the structure and coupling features of the plates, fourplate embodiments are illustrated and described herein, although othersuitable plate embodiments can be used with the invention. Each of thefour plate embodiments has the above described convex mesh on itsoutwardly facing surface, although other vertebral body attachmentdevices and mechanisms can be used without departing from the scope ofthe invention. Each of the four plate embodiments has a differentinwardly facing surface from the other three plate embodiments. Thefirst plate embodiment ahs a flat inwardly facing surface that accepts afastener (e.g., rivet, plug, dowel, or screw; a rivet is used herein asan example) for securing a narrow end of the spider spring thereto,rotatably or otherwise. The second plate embodiment has a circularrecess on its inwardly facing surface, for rotationally housing a wideend of a spider spring and allowing the wide end to expand in unrestricted fashion when the spider spring is compressed. The third plateembodiment has a semispherical (e.g., ball-shaped) protuberance on itsinwardly facing surface, for rotatably and angulatably holding a narrowend of a spider spring, which narrow end includes a curvate sockethaving a substantially constant radius of curvature that is alsosubstantially equivalent to the radius of the ball-shaped protuberance.The fourth plate embodiment has such a curvate socket on its inwardlyfacing surface, for rotatable and angulatably holding a narrow end of aspider spring, which narrow end includes a ball-shaped protuberancesimilar to that described above.

Each ball-shaped protuberance has an axial bore that receives adeflection preventing element (e.g., rivet, plug, dowel, or screw; arivet is used herein as an example). prior to the insertion of therivet, the ball-shaped protuberance can deflect radially inward (so thatthe ball-shaped protuberance contracts). The insertion of the riveteliminates the capacity for this deflection. The curvate socket, havinga substantially constant radius of curvature that is also substantiallyequivalent to the radius of the ball-shaped protuberance, accommodatesthe ball-shaped protuberance for free rotation and angulation once theball-shaped protuberance is disposed in the curvate socket, but in theball-shaped protuberance's undeflected state, the ball-shapedprotuberance cannot fit through the opening leading to the curvatesocket. Therefore, the deflectability of the ball-shaped protuberance,prior to the insertion of the rivet, permits the ball-shapedprotuberance to be inserted into the curvate socket. Subsequentintroduction of the rivet into the axial bore of the ball-shapedprotuberance prevents the ball-shaped protuberance from deflecting, andthus prevents the ball-shaped protuberance from escaping the socket.Thereby, the ball-shaped protuberance can be secured in the curvatesocket to that it rotates and angulates therein through a range ofangles, thus permitting the plates to rotate and angulate relative toone another through a corresponding range of angles equivalent to thefaction of normal human spine rotation and angulation (to mimic normaldisc rotation and angulation).

With the four plate embodiments, the various spider spring embodiments,and the several manners in which they may be coupled together, it ispossible to assemble a variety of artificial disc embodiments. Manyexamples are described herein, although many permutations that arecontemplated and encompassed by the invention are not specificallyidentified herein, but are readily identifiable with an understanding ofthe invention as described. For example, all spider springs having acurvate socket can be coupled with a ball-shaped protuberance on eitheranother spider spring or a plate. Also for example, all spider springshaving a ball-shaped protuberance can be coupled with a curvate socketon either a spider spring or another plate, or with a bored central hubof a spider spring. Also for example, all plates having a curvate socketcan be coupled with a ball-shaped protuberance on either another plateor a spider spring. Also for example, all plates having a ball-shapedprotuberance can be coupled with a curvate socket on either anotherplate or a spider spring. Also for example, all spider springs without aball-shaped protuberance or a curvate socket can be coupled with a flatinwardly facing surface of a plate. Also for example, each wide end ofeach spider spring can be coupled with a circular recess of a plate, anda shield can be secured over the spider spring after it has been placedin the circular recess to prevent the spider spring from escaping therecess when a tension load is applied to the plates.

Each assembly with a spider spring enjoys spring-like performance withrespect to axially compressive loads, as well as long cycle life tomimic the axial biomechanical performance of the normal humanintervertebral disc. The separate spring arms of the spider spring allowthe spider spring to expand radially as the spring arms further separateunder the compressive load, only to spring back into its undeflectedshape when it is unleaded. As the spider spring compresses anddecompresses, the alls of the circular recess of the second plateembodiment maintain the wide end of the spider spring within aprescribed boundary on the inwardly facing surface of the plate. Theassemblies withstand tension loads on the outwardly facing surfaces,because (in embodiments having a spider spring) the shield retains thewide end in the circular recess and because (in embodiments having theball-shaped protuberance) the rivet in the axial bore prevents theball-shaped protuberance from deflecting, thus preventing it fromexiting the curvate socket when the artificial disc is under a tensionload and because (in embodiments in which the narrow end of a spiderspring is secured by a rivet), the flanged portion of the rivet securingthe narrow end of the spider spring prevents the spider spring fromseparating from the post portion of the rivet. Accordingly, once theplates are secured to the vertebral bones, the assembly will not comeapart when a normally experienced tension load is applied to the spine,similar to the tension-bearing integrity of a healthy naturalintervertebral disc.

Assemblies having the ball-and-socket joint also provide a centroid ofmotion centrally located within the intervertebral space, because theplates are made rotatable and angulatable relative to one another by theball-shaped protuberance being rotatably and angulatably coupled in thecurvate socket. The centroid of motion remains in the ball-shapedprotuberance, and thus remains centrally located between the vertebralbodies, similar to the centroid of motion in a healthy naturalintervertebral disc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1.1 through 1.9 show various embodiments of plates of theinvention for use in an artificial disc of the invention.

FIGS. 1.1 and 1.2 show a bottom plan view and a side cutaway view,respectively, of a plate having a flat surface on its inwardly facingsurface.

FIGS. 1.3 and 1.4 show a bottom plan view and a side cutaway view,respectively, of a plate having a circular recess on its inwardly facingsurface.

FIGS. 1.5 and 1.6 show a bottom plan view and a side cutaway view,respectively, of a plate having a ball-shaped protuberance on itsinwardly facing surface.

FIGS. 1.7 and 1.8 show a bottom plan view and a side cutaway view,respectively, of a plate having a curvate socket on its inwardly facingsurface.

FIG. 1.9 shows a top plan view of any of the plates of FIGS. 1.1 through1.8 (all appear the same from this view).

FIGS. 2.1 through 2.12 show top view of various embodiments of spidersprings of the invention for use in an artificial disc of the invention,to illustrate a variety of spring arm configurations and central hubfeatures contemplated by the invention.

FIG. 2.1 shows a spider spring having a solid central hub and springarms with radially parallel sides.

FIG. 2.2 shows a spider spring having a solid central hub and springarms with radially outwardly diverging sides.

FIG. 2.3 shows a spider spring having a solid central hub and springarms with radially outwardly diverging and curving sides.

FIG. 2.4 shows a spider spring having a bored central hub and springarms with radially parallel sides.

FIG. 2.5 shows a spider spring having a bored central hub and springarms with radially outwardly diverging sides.

FIG. 2.6 shows a spider spring having a bored central hub and springarms with radially outwardly diverging and curving sides.

FIG. 2.7 shows a spider spring having a central curvate socket andspring arms with radially parallel sides.

FIG. 2.8 shows a spider spring having a central curvate socket andspring arms with radially outwardly diverging sides.

FIG. 2.9 shows a spider spring having a central curvate socket andspring arms with radially outwardly diverging and curving sides.

FIG. 2.10 shows a spider spring having a central ball-shapedprotuberance and spring arms with radially parallel sides.

FIG. 2.11 shows a spider spring having a central ball-shapedprotuberance and spring arms with radially outwardly diverging sides.

FIG. 2.12 shows a spider spring having a central ball-shapedprotuberance and spring arms with radially outwardly diverging andcurving sides.

FIGS. 3.1 through 3.12 show side cross-section views of variousembodiments of spider springs of the invention for use in an artificialdisc of the invention, to illustrate additional varieties of spring armconfigurations and central hub features of the invention.

FIG. 3.1 shows a spider spring having downwardly extending and radiallystraight spring arms.

FIG. 3.2 shows a spider spring having downwardly extending and radiallybowed spring arms.

FIG. 3.3 shows a spider spring having radially straight spring arms,some of which are downwardly extending and some of which are upwardlyextending.

FIG. 3.4 shows a spider spring having radially bowed spring arms, someof which are downwardly extending and some of which are upwardlyextending.

FIG. 3.5 shows a spider spring having radially straight spring arms,each having a lower downwardly extending portion and an upper upwardlyextending portion.

FIG. 3.6 shows a spider spring having radially bowed spring arms, eachhaving a lower downwardly extending portion and an upper upwardlyextending portion.

FIG. 3.7 shows a spider spring having downwardly extending and radiallystraight spring arms and a bored central hub.

FIG. 3.8 shows a spider spring having downwardly extending and radiallybowed spring arms and a bored central hub.

FIG. 3.9 shows a spider spring having downwardly extending and radiallystraight spring arms and a central curvate socket.

FIG. 3.10 shows a spider spring having downwardly extending and radiallybowed spring arms and a central curvate socket.

FIG. 3.11 shows a spider spring having downwardly extending and radiallystraight spring arms and a central ball-shaped protuberance.

FIG. 3.12 shows a spider spring having downwardly extending and radiallybowed spring arms and a central ball-shaped protuberance.

FIGS. 4.1 through 4.20 show side cross=section views, end cross-sectionview, and top views of spring arms of various embodiments of spidersprings, to illustrate additional varieties of spring arms of theinvention.

FIG. 4.1 shows a straight spring arm that is radially wavy.

FIG. 4.2 shows a straight spring arm that is radially thinning.

FIG. 4.3 shows a straight spring arm that is radially thickening.

FIG. 4.4 shows a straight spring arm that is concentrically grooved,with grooves that are similarly dimensioned to one another regardless oftheir relative radial distance from the central hub.

FIG. 4.5 shows a straight spring arm that is concentrically grooved,with grooves that become smaller with a greater radial distance of thegroove from the central hub.

FIG. 4.6 shows a straight spring arm that is concentrically grooved,with grooves that become larger with a greater radial distance of thegroove from the central hub.

FIG. 4.7 shows a bowed spring arm that is radially wavy.

FIG. 4.8 shows a bowed spring arm that is radially thinning.

FIG. 4.9 shows a bowed spring arm that is radially thickening.

FIG. 4.10 shows a bowed spring arm that is concentrically grooved, withgrooves that are similarly dimensioned to one another regardless oftheir relative radial distance from the central hub.

FIG. 4.11 shows a bowed spring arm that is concentrically grooved, withgrooves that become smaller with a greater radial distance of the groovefrom the central hub.

FIG. 4.12 shows a bowed spring arm that is concentrically grooved, withgrooves that become larger with a greater radial distance of the groovefrom the central hub.

FIG. 4.13 shows a spring arm having an extent that is concentricallystraight.

FIG. 4.14 shows a spring arm having an extent that is concentricallywavy.

FIG. 4.15 shows a spring arm having an extent that is radially grooved.

FIG. 4.16 shows a spring arm having an extent that is concentricallybowed, with the concave surface facing down.

FIG. 4.17 shows a spring arm having an extent that is concentricallybowed, with the concave surface facing up.

FIG. 4.18 shows a spider spring having spring arms with concentricgrooves having a concentrically varying width, wherein the concentricgrooves collectively form two macro concentric grooves across all of thespring arms.

FIGS. 4.19 and 4.20 show a spider spring having at least one spring armwith a radial groove that varies in width and depth along the length ofthe groove.

FIGS. 5.1 through 5.8 show side views of various assembled artificialdisc embodiments of the invention, with plates and shields of theinvention in side cutaway view, but spider springs of the invention inside cross-section view.

FIG. 5.1 shows a spider spring having a solid central hub, with itscentral hub riveted to a flat surface of an upper plate and its wide endseated within a circular recess of a lower plate.

FIG. 5.2 shows a spider spring having a bored central hub, with itscentral hub rotatably secured by a flanged rivet to a flat surface of anupper plate and its wide end seated within a circular recess of a lowerplate.

FIG. 5.3 shows a spider spring having a central curvate socket, with itscurvate socket coupled to a ball-shaped protuberance of an upper plateand its wide end seated within a circular recess of a lower plate.

FIG. 5.4 shows a spider spring having a central ball-shapedprotuberance, with its ball-shaped protuberance coupled to a curvatesocket of an upper plate and its wide end seated within a circularrecess of a lower plate.

FIG. 5.5 shows a spider spring having two wide ends, with its top wideend seated within a circular recess of an upper plate, and its bottomwide end seated within a circular recess of a lower plate.

FIG. 5.6 shows two spider springs, a bottom one having a central curvatesocket and a top one having a central ball-shaped protuberance, with thecurvate socket and the ball-shaped protuberance coupled together, andwith the wide end of the tope spider spring seated within a circularrecess of an upper plate, and the wide end of the bottom spider springseated within a circular recess of a lower plate.

FIG. 5.7 shows two spider springs, a bottom one having a bored centralhub and a top one having a central ball-shaped protuberance, with thebored central hub and the ball-shaped protuberance coupled together, andwith the wide end of the top spider spring seated within a circularrecess of an upper plate, and the wide end of the bottom spider springseated within a circular recess of a lower plate.

FIG. 5.8 shows a lower plate having a central curvate socket and anupper plate having a central ball-shaped protuberance, with the curvatesocket and the ball-shaped protuberance coupled together.

FIG. 6 shows a side perspective view of a prior art interbody fusiondevice.

FIG. 7 shows a front view of the anterior portion of the lumbo-sacralregion of a human spine, into which a pair of interbody fusion devicesof FIG. 6 have been implanted.

DETAILED DESCRIPTION

While the invention will be described more fully hereinafter withreference to the accompanying drawings, in which particular embodimentsand methods of implantation are shown, it is to be understood at theoutset that persons skilled in the art may modify the invention hereindescribed while achieving the functions and results of the invention.Accordingly, the descriptions that follow are to be understood asillustrative and exemplary of specific structures, aspects and featureswithin the broad scope of the invention and not as limiting of suchbroad scope. Like numbers refer to similar features of like elementsthroughout.

Referring now to FIGS. 1.1 through 1.9, various embodiments of plates ofthe invention for use in an artificial disc of the invention are shownin bottom plan views (FIGS. 1.1, 1.3, 1.5 and 1.7), side cutaway views(where cross-sectional areas and surfaces viewable behind them areshown) (FIGS. 1.2, 1.4, 1.6 and 1.8), and a top plan view (FIG. 1.9).More specifically, FIGS. 1.1 and 1.2 show a bottom plan view and a sidecutaway view, respectively, of a first embodiment 100 a of a plate.FIGS. 1.3 and 1.4 show a bottom plan view and a side cutaway view,respectively, of a second embodiment 100 b of a plate. FIGS. 1.5 and 1.6show a bottom plan view and a side cutaway view, respectively, of athird embodiment 100 c of a plate. FIGS. 1.7 and 1.8 show a bottom planview and a side cutaway view, respectively, of a fourth embodiment 100 dof a plate. FIG. 1.9 shows a top plan view of any of the plates 100 a-d(all appear the same from this view). As will be described in greaterdetail below, depending on the type of spider spring used in aparticular embodiment of an artificial disc of the invention, two platesselected (for the manner in which they cooperate with the type of spiderspring used in the embodiment) from these four embodiments will be usedas opposing plates of the embodiment. Some embodiments of the artificialdisc use two plates of the same plate embodiment.

Each plate 100 a-d has an exterior surface 108 a-d. Because theartificial disc of the invention is to be positioned between the facingsurface of adjacent vertebral bodies, the two plates used in theartificial disc are disposed such that the exterior surfaces face awayfrom one another (as best seen in FIGS. 5.1 through 5.8, discussedbelow). The two plates are to mate with the vertebral bodies so as tonot rotate relative thereto, but rather to permit the spinal segments toaxially compress and bend relative to one another in manners that mimicthe natural motion of the spinal segment. This motion is permitted bythe performance of a spider spring (described below) disposed betweenthe secured plates. The mating of the plates to the vertebral bodies andthe application of the spider spring to the plates are described below.

More particularly, each plate 100 a-d is a flat plate (preferably madeof a metal such as, for example, titanium) having an overall shape thatconforms to the overall shape of the respective endplate of thevertebral body with which it is to mate. Further, each plate 100 a-dcomprises a vertebral body contact element (e.g., a convex mesh 106 a-d)(preferably oval in shape) that is attached to the exterior surface 108a-d of the plate 100 a-d to provide a vertebral body contact surface.The mesh 106 a-d is secured at its perimeter, by laser welds, to theexterior surface 108 a-d of the plate 100 a-d. The mesh is domed in itsinitial undeflected conformation, but deflects as necessary duringinsertion of the artificial disc between vertebral bodies, and, once theartificial disc is seated between the vertebral bodies, deforms asnecessary under anatomical loads to reshape itself to the concavesurface of the vertebral endplate. This affords the plate having themesh substantially superior gripping and holding strength upon initialimplantation as compared with other artificial disc products. The meshfurther provides an osteoconductive surface through which the bone myultimately grow. The mesh is preferably comprised of titanium, but canalso be formed from other metals and/or non-metals without departingfrom the scope of the invention.

Each plate 100 a-d further comprises at least a lateral ring 110 a-dthat is osteoconductive, which may be, for example, a sprayed depositionlayer, or an adhesive applied beaded metal layer, or another suitableporous coating. This porous ring permits the long-term ingrowth ofvertebral bone into the plate, thus permanently securing the prosthesiswithin the intervertebral space. It shall be understood that this porouslayer 110 a-d may extend beneath the domed mesh 106 a-d as well, but ismore importantly applied to the lateral rim of the exterior surface 108a-d of the plate 100 a-d that seats directly against the vertebral body.

It should be understood that the convex mesh attachment devices andmethods described herein can be used not only with the artificial discsan artificial disc plates described or referred to herein, but also withother artificial discs and artificial disc plates, including, but notlimited to, those currently known in the art. Therefore, the descriptionof the mesh attachment devices and methods being used with theartificial discs and artificial disc plates described or referred toherein should not be construed as limiting the application and/orusefulness of the mesh attachment device.

With regard to the disposition of a spider spring between two plates,each of the plates 100 a-d comprises features for applying the spiderspring thereto, and the various application methods are described below.More specifically, the first plate embodiment 100 a includes an inwardlyfacing surface 104 a that includes a flat surface 102 a that accepts afastener (e.g., rivet, plug, dowel, or screw; a rivet 114 a is usedherein as an example) (shown in FIG. 5.1) for securing a narrow end of aspider spring thereto, rotatably or otherwise.

The second plate embodiment 100 b includes an inwardly facing surface104 b that includes a circular recess 102 b for rotationally housing awide end of a spider spring and allowing the wide end to expand inunrestricted fashion when the spider spring is compressed, and theinwardly facing surface 104 b also accepts fasteners (e.g., rivets,plugs, dowels, or screws; rivet 116 b are used herein as examples)(shown in FIGS. 5.1 through 5.7) for securing a shield 118 b (thepurpose and application of the shield are described below and shown onFIGS. 5.1 through 5.7).

The third plate embodiment 100 c includes an inwardly facing surface 104c that includes an inwardly directed semispherical (e.g., ball-shaped)protuberance 102 c. The ball-shaped protuberance 102 c includes a seriesof slots 120 c that render the ball-shaped protuberance 102 c radiallycompressible and expandable in correspondence with a radial pressure (ora radial component of a pressure applied thereto). The ball-shapedprotuberance 100 c further includes an axial bore 122 c that accepts adeflection preventing element (e.g., rivet, plug, dowel, or screw; arivet 124 c is used herein as an example) (shown in FIGS. 5.3 and 5.8).(Alternatively, the axial bore can be threaded to accept a screw.) Priorto the insertion of the rivet 124 c, the ball-shaped protuberance 102 ccan deflect radially inward because the slots 120 c will narrow under aradial pressure. The insertion of the rivet 124 c eliminates thecapacity for this deflection. Therefore, the ball-shaped protuberance102 c, before receiving rivet 124 c, can be compressed to seat in acurvate socket portion of a spider spring and, once the ball-shapedprotuberance 102 c has been seated in the curvate socket, the rivet 124c can be inserted into the axial bore 122 c to ensure that theball-shaped protuberance 102 c remains held in the curvate socket. Ahole can be provided in the opposing plate so that the interior of thedevice may be readily accessed if a need should arise.

The fourth plate embodiment 199 d includes an inwardly facing surface104 d that includes a central curvate socket 102 d for receiving thereina ball-shaped protuberance of the type described above. Not only can thecurvate socket 102 d accept the ball-shaped protuberance 102 c of thethird plate embodiment 100 c, but (as will be discussed below) thecurvate socket 102 d can accept a similar ball-shaped protuberance on anarrow end of a spider spring. Each curvate socket (whether on a plateor on a narrow end of a spider spring) has a substantially constantradius of curvature that is also substantially equivalent to the radiusof the ball-shaped protuberance with which it mates, so that when theball-shaped protuberance is secured therein, the ball-shapedprotuberance can rotate and angulate freely relative to the curvatesocket through a range of angles, thus permitting the opposing plates torotate and angulate freely relative to one another through acorresponding range of angles equivalent to the fraction of normal humanspine rotation and angulation (to mimic normal disc rotation andangulation).

Referring now to FIGS. 2.1 through 2.12, top view of various embodimentsof spider spring of the invention for use in an artificial disc of theinvention are shown to illustrate a variety of spring arm configurationsand central hub features that are merely a subset of the spring armconfigurations and central hub features contemplated by the invention.More specifically, each spider spring (e.g., 200 a 1-12) has spring arms(e.g., 202 a 1-12), with arm sides (e.g., 208 a 1-12), extendingradially from a central hub (e.g., 204 a 1-12) such that arm separationspaces (e.g., 203 a 1-12) are formed. In some embodiments (e.g., 200 a1-d 2), the spring arms (e.g., 202 a 1-d 2) have radially parallel sides(e.g., 208 a 1-d 2), forming radially widening arm separation spaces(e.g., 203 a 1-d 2). In other embodiments (e.g., 200 e 1-h 2), thespring arms (e.g., 202 e 1-h 2) have radially outwardly diverging sides(e.g., 208 e 1-h 2), forming radially parallel arm separation spaces(e.g., 203 e 1-h 2). In other embodiments (e.g., 200 i 1-l 2), thespring arms (e.g., 202 i 1-l 2) have radially outwardly diverging andcurving sides (e.g., 208 i 1-l 2), forming curved arm separation spaces(e.g., 203 i 1-l 2). The number and shape of the spring arms, and theformation of the resulting arm separation spaces, can be varied toaccommodate any desired application, inasmuch as varying the dimensionswill affect the expansion and retraction behavior of the spider spring.

Generally, as a compressive load is applied to a spider spring, theforces are directed into a hoop stress that causes the spring arms tomove radially outwardly and the arms separation spaces to expand. Thishoop stress is counterbalanced by the material strength of the spiderspring, and the strain of the material causes a deflection in the heightof the spider spring. Stated equivalently, a spider spring responds to acompressive load by deflecting compressively, but provides a restoringforce that is proportional to the elastic modulus of the material in ahoop stressed condition. It should be understood that spider springsother than those shown are contemplated by the invention, including butnot limited to spider springs having more or fewer arms, and includingspider springs having arms configured differently than hose shown (e.g.,with radially outwardly converging sides), and including spider springshaving at least two arms that are configured differently from oneanother.

With regard to the central hub features shown on FIG. 2.1 through 2.12,these are discussed in greater detail below with reference to FIGS. 5.1through 5.7 regarding methods of applying spider springs to the platesdiscussed above. However, for properly understanding the discussions ofFIGS. 3.1 through 3.12 and 4.1 through 4.20, it is important tosummarize here that some spider spring embodiments (e.g., 200 a 1-a 6,41-e 6, i 1-i 6) have solid hubs (e.g., 204 a 1-a 6, e 1-e 6, i 1-i 6),other spider spring embodiments (e.g., 200 b 1-b 2, f 1-f 2, j 1-j 2)have on their central hubs (e.g., 204 b 1-b 2, f 1-f 2, j 1-j 2) a bore(e.g., 206 b 1-b 2, f 1-f 2, j 1-j 2), still other spider springembodiments (e.g., 200 c 1-c 2, g 1-g 2, k 1-k 2) have on their centralhubs (e.g., 204 c 1-c 2, g 1-g 2, k 1-k 2) curvate sockets (e.g., 206 c1-c 2, g 1-g 2, k 1-k 2) similar to those described as being on plateembodiment 100 d, and still other spider spring embodiments (e.g., 200 d1-d 2, h 1-h 2, l 1-l 2) have on their central hubs (e.g., 204 d 1-d 2,h 1-h 2, l 1-l 2) ball-shaped protuberances (e.g., 206 d 1-d 2, h 1-h 2,l 1-l 2) similar to those described as being on plate embodiment 100 c.

Referring now also to Figures 3.1 through 3.12, side cross-section views(where only the cross-sectional area is shown) of various embodiments ofspider springs are shown to illustrate additional varieties of springarm configurations and central hub features that are merely a subset ofthe spring arm configurations and central hub features contemplated bythe invention. The side cross-sections are taken along cut lines A-A′,B-B′, C-C′, D-D′, E-E′, F-F′, G-G′, H-H′, I-I′, J-J′, K-K′, and L-L′ onFIGS. 2.1 through 2.12, as applicable. It should be understood that asingle cross-section view can illustrate more than one spider springembodiment, given that some spider springs look similar from a top viewbut not similar from a side cross-section view. For example, FIGS. 3.1through 3.6 illustration spider spring embodiments that from a top viewappear as any of FIGS. 2.1 through 2.3. Also, for example, FIGS. 3.7 and3.8 illustrate spider spring embodiments that from a top view appear asany of FIGS. 2.4 through 2.6. Also, for example, FIGS. 3.9 and 3.10illustrate spider spring embodiments that from a top view appear as anyof FIGS. 2.7 through 2.9. And, for example, FIGS. 3.11 and 3.12illustrate spider spring embodiments that from a top view appear as anyof FIGS. 2.10 through 2.12. Multiple reference numbers for elements inFIGS. 3.1 through 3.12 are used to identify these multiple permutationpossibilities. Stated alternatively, each of FIGS. 3.1 through 3.12 isnot a side cross-section view that is associated with only one of thetop views of FIGS. 2.1 through 2.12, but rather is associatable withmore than one of the tope views of FIGS. 2.1 through 2.12.

More specifically, FIGS. 3.1, 3.3, 3.5, 3.7, 3.9, and 3.11 showconfigurations where the extents of spring arms (e.g., 202 a 1,e 1,i 1,a 3,e 3,i 3, a 5,e 5,i 5, b 1,f 1,j 1, c 1,g 1,k 1, d 1,h 1,l 1) areradially straight such that the height of the spider spring (e.g., 200 a1,e 1,i 1, a 3,e 3,i 3 a 5,e 5,i 5, b 1,f 1,j 1, c 1,g 1,k 1, d 1,h 1,l1) is linearly related to the radial length of the spring arms. FIGS.3.2, 3.4, 3.6, 3.8, 3.10, and 3.12 show configurations where the extentsof the spring arms (e.g., 202 a 2,e 2,i 2, a 4,e 4,i 4, a 6,e 6,i 6, b2,f 2,j 2, c 2,g 2,k 2, d 2,h 2,l 2) are radially bowed, such that theheight of the spider spring (e.g., 200 a 2,e 2,i 2, a 4,e 4,i 4, a 6,e6,i 6, b 2,f 2,j 2, c 2,g 2,k 2, d 2,h 2,l 2) is not linearly related tothe radial length of the spring arms (but rather the spider spring may,for example, be parabolic in shape). FIGS. 3.1, 3.2, and 3.7 through3.12 show configurations in which the spring arms (e.g., 202 a 1-a 2, b1-e 2, f 1-i 2, j 1-l 2) extend radially downward from the central hub(e.g., 204 a 1-a 2, b 1-e 2, f 1-i 2, j 1-l 2). FIGS. 3.5 and 3.6 showconfigurations in which the spring arms (e.g., 202 a 5-a 6, e 5-e 6, i5-i 6) are doubled, with lower portions extending radially downwardlyfrom the central hub (e.g., 204 a 5-a 6, e 5-e 6, i 5-i 6) and upperportions extending radially upwardly from the central hub. As will bediscussed below, it is possible to achieve a similar double spring armconfiguration by mounting a balled spider spring (e.g., 200 d 1-d 2, h1-h 2, l 1-l 2) to a bored spider spring (e.g., 200 b 1-b 2, f 1-f 2, j1-j 2) to create a spring comprising opposing spider springs rotatingand angulating with respect to one another about the resultingball-and-bore joint at their narrow ends. Further, as will be discussedbelow, it is also possible to achieve a similar double spring armconfiguration by mounting a balled spider spring (e.g., 200 d 1-d 2, h1-h 2, l 1-l 2) to a socketed spider spring (e.g., 200 c 1-c 2, g 1-g 2,k 1-k 2) to create a spring comprising opposing spider springs rotatingand angulating with respect to one another about the resultingball-and-socket joint at their narrow ends. FIGS. 3.3 and 3.4 showconfigurations in which some of the spring arms (e.g., 202 a 3-a 4, e3-e 4, i 3-i 4) extend radially downwardly from the central hub (e.g.,204 a 3-a 4, e 3-e 4, i 3-i 4) and others of the spring arms extendradially upwardly from the central hub. Preferably, as in theconfigurations shown in FIGS. 3.3 and 3.4, the upwardly extending springarms and the downwardly extending spring arms alternate.

Further with regard to the central hub features shown in top views onFIGS. 2.1 through 2.12, these are shown in side cross-section views inFIGS. 3.1 through 3.12. More specifically, the solid central hubs (e.g.,204 a 1-a 6, e 1-0 e 6, i 1-i 6) are shown in FIGS. 3.1 through 3.6. Thebored central hubs (e.g., 204 b 1-b 2, f 1-f 2, j 1-j 2) are shown inFIGS. 3.7 and 3.8. The curvate sockets (e.g., 206 c 1-c 2, g 1-g 2, k1-k 2) are shown in FIGS. 3.9 and 3.10. The ball-shaped protuberances(e.g., 206 d 1-42, h 1-h 2, l 1-l 2) are shown in FIGS. 3.11 and 3.12.It should be understood that the specific dimensions of the ball-shapedprotuberance, the mechanism for radial compressibility of theball-shaped protuberance, and the mechanism for preventing radialcompression of the ball-shaped protuberance are not limited to thoseshown, but rather can be varied and changed without departing from thescope of the invention.

Referring now also to FIGS. 4.1 through 4.12, side cross-section views(where only the cross-sectional area is shown) of spring arms (e.g., 202m 1-n 6) of various embodiments of spider springs are shown toillustrate additional varieties of spring arm configuration that aremerely a subset of the spring arm configurations contemplated by theinvention. The side cross-sections are taken from the base of the springarm (i.e., the portion that connects with the central hub) radially tothe outermost edge of the spring arm. It should be understood that withregard to the remaining structure of the spider springs having theillustrated circumferential extents, the spider springs can share all orsome of the features (e.g., spring arm configurations, arm sideconfigurations, arm separation space configurations, number of springarms, direction of spring arms, central hub configurations, etc.) of theother spider spring embodiments discussed herein, and/or have featuresthat are different and/or configured differently.

More specifically, FIGS. 4.1 through 4.12 show configurations where theextents of the spring arms are generally radially straight (FIGS. 4.1through 4.6), such that the height of the spider spring is linearlyrelated to the radial length of the spring arms, or generally radiallybowed (FIGS. 4.7 through 4.12), such that the height of the spiderspring is not linearly related to the radial length of the spring arms,but additionally have at least one concentric or radial characteristicthat alters the performance of the spider spring in expansion and/orretraction. For example, the spring arms in FIGS. 4.1 and 4.7 areradially wavy. Also for example, the spring arms in FIGS. 4.2 and 4.8are radially thinning (the portion of the arm near the central hub isthicker than the portion of the arm near the outer edge of the arm).Also for example, the spring arms in FIGS. 4.3 and 4.9 are radiallythickening (the portion of the arm near the central hub is thinner thanthe portion of the arm near the outer edge of the arm). Also forexample, the spring arms in FIGS. 4.4, 4.5, 4.6, 4.10, 4.11 and 4.12 areconcentrically grooved, having grooves that are similarly dimensioned toone another regardless of their relative radial distance from thecentral hub (FIGS. 4.4 and 4.10), or grooves that vary in dimension fromone another depending on their relative radial distance from the centralhub (FIGS. 4.5, 4.6, 4.11 and 4.12). For example, the width and depth ofthe grooves in FIG. 4.5 and the grooves in FIG. 4.11 become smaller withthe greater radial distance of the groove from the central hub. And, forexample, the width and depth of the grooves in FIG. 4.6 and the groovesin FIG. 4.12 become larger with the greater radial distance of thegroove from the central hub.

In some spring arm embodiments, at least one dimension of a concentricgroove (such as, for example, the width and/or depth) can be applied tovary concentrically across the spring arm. Further, in some embodiments,the concentric grooves can be applied to the spring arms of a spiderspring embodiment in a macro pattern, where the concentric grooves oneach individual arm extend from one arm to another to form one or moremacro concentric grooves, each of which extends across all or some ofthe spring arms. FIG. 4.18 shows one example of a configuration wheretwo macro concentric grooves, each concentrically varying in width, areapplied to the spring arms of a spider spring embodiment 200 p.

Referring now also to FIGS. 4.13 through 4.17, end cross-section views(where only the cross-sectional area is shown) of spring arms (e.g., 202o 1-o 5) of various embodiments of spider springs are shown toillustrate additional varieties of spring arm configurations that aremerely a subset of spring arm configurations contemplated by theinvention. The end cross-sections are taken from one side of the springarm to the other (i.e., perpendicular to the side cross-sectionsdiscussed above with regard to FIGS. 4.1 through 4.12). It should beunderstood that with regard to the remaining structure of the spidersprings having the illustrated circumferential extents, the spidersprings can share all or some of the features (e.g., spring armconfigurations, arms side configurations, arm separation spaceconfigurations, number of spring arms, direction of spring arms, centralhub configurations, etc.) of the other spider spring embodimentsdiscussed herein, and/or have features that are different and/orconfigured differently.

More specifically, FIG. 13 shows a spring arm configuration where theextent of the arm is concentrically uniform, whereas FIGS. 4.14 through4.17 show spring arm configurations where the extents of the spring armshave at least one concentric or radial characteristic that alters theperformance of the spider spring in expansion and/or retraction, ascompared to the spring arm configurations of FIG. 13. For example, thespring arm in FIG. 4.15 is radially grooved. The spring arm in FIG. 4.16is radially bowed, with the concave surface facing down. The spring armin FIG. 4.17 is radially bowed, with the concave surface facing up.

It should be noted that with regard to spring arms having at least oneradial groove (e.g., FIG. 4.15), one or both of the depth and the widthof each groove can be (1) decreasing along the length of the groove fromthe outer edge of the spring arm toward the central hub, (2) increasingalong the length of the groove from the outer edge of the spring armtoward the central hub, (3) uniform along the length of the groove fromthe outer edge of the spring arm toward the central hub, or (4) variedalong the length of each groove from the outer edge of the spring armtoward the central hub, either randomly or according to a pattern. Aspider spring embodiment 2001 having a spring arm 202 q with a radiallygrooved configuration, as an example of case (1), is shown in top viewin FIG. 4.19 and in spring arm side cross-section view in FIG. 4.20(taken along cut lines !-!′ in FIG. 4.19), where both the width anddepth of a groove 212 q vary along the length of the groove. Moreover,it can be the case that each groove is not formed similarly to one ormore other grooves (on the same spring arm or other spring arms), butrather one or more grooves are formed in any of the above-mentionedfashions, while one or more other grooves are formed in another of theabove-mentioned fashions or other fashions. It should be clear that anygroove pattern can be implemented without departing from the scope ofthe invention.

It should be understood that the spring arms contemplated by theinvention include, but are not limited to, those having only oneconcentric or radial characteristic at a time. The use of more than oneconcentric or radial characteristic per arm is contemplated, as well asthe use of concentric and radial characteristics simultaneously.Further, it is contemplated that some spider spring embodiments will useonly radially straight arms, some spider spring embodiments will useonly radially bowed arms, and some spider spring embodiments that willuse both radially straight arms as well as radially bowed arms.

Referring again to FIGS. 2.1 through 2.12, each of the spider springs issuitable for disposition between two opposing plates of the invention.As noted above, and as discussed in greater detail below, depending onthe type of spider spring used in the particular embodiment of theartificial disc of the invention, the two plates are selected (for themanner in which they cooperate with the type of spider spring used inthe embodiment) from the four plate embodiments, for use as opposingplates of the embodiment. Some embodiments of the artificial disc usetwo plates of the same plate embodiment. In each embodiment, the plateare made rotatable and angulatable relative to one another (to mimic thefunctionality of a healthy natural intervertebral disc) by having aspring member, and/or by the manner in which the spring member issecured to one or more of the plates, and/or by the manner in which twospring members are secured to one another, or by the manner in which theplates are secured to one another. Further in each embodiment, the samecouplings, and/or through the use of additional coupling elements (e.g.,shields and/or rivets and/or screws), enable the artificial discembodiments to withstand tension loading (to mimic the functionality ofa healthy natural intervertebral disc). Further in embodiments having aspring member, the spring member enables the artificial disc embodimentsto axially compress and axially restore (to mimic the functionality of ahealthy natural intervertebral disc).

Referring now also to FIGS. 5.1 through 5.8, these figures show sideviews of various assembled artificial disc embodiments contemplated bythe invention. The side views show the plates in side cutaway view, butthe spider springs in side cross-section view. It should be understoodthat the illustrated embodiments do not encompass all embodimentcontemplated by the invention, but rather were selected for illustrationpurposes to show how the features of the various illustrated plateembodiments cooperate with corresponding features of the variousillustrated spider spring embodiments, when the spider springs aredisposed between opposing plates of the invention. While only certainassembled artificial disc embodiments are shown, it should be understoodthat spider springs not shown but having like plate coupling featurescan be secured to cooperating plates in the manner illustrated, invarious permutations and combinations, and the same have been withheldfrom illustration for purposes of conciseness and clarity only to avoidduplicative illustration that would only visually reiterate that whichcan be understood from the descriptions herein.

For example, and referring to FIG. 5.1, some spider springs (e.g.,spider springs 200 a 1-a 2, e 1-e 2, i 1-i 2) are designed to have thenarrow end of the spider spring secured to a flat surface on an inwardlyfacing surface of a plate (e.g., the flat surface 102 a on the inwardlyfacing surface 104 a of plate 100 a), preferably those spider springs inwhich all of the spring arms extend downwardly or in which all of thespring arms extend upwardly (for both see, e.g., FIGS. 3.1 and 3.2 forside cross-section views of exemplary embodiments), both in contrast tohaving some spring arms extending downwardly and others extendingupwardly (see, e.g., FIGS. 3.3 through 3.6). These spider springspreferably have a solid central hub (e.g., 204 a 1-a 2, e 1-e 2, i 1-i2) that can be secured against the flat surface of the plate, e.g., by afastener (e.g., rivet, plug, dowel, or screw; a rivet 114 a is usedherein as an example) (shown in FIG. 5.1). (if a screw is used, athreaded bore can be provided in the plate for its acceptance.) Therivet 114 a prevents rotation of the spider spring relative to the plateagainst which it is secured, but as also discussed below with regard tothe securing of the wide end of the spider spring, the plates arerotatable relative to one another because the wide end of the spiderspring can rotate with respect to the plate having the circular recessin which the wide end seats (discussed below). Further, the plates areangulatable relative to one another because the spring arms of thespider spring can individually compress and restore, enabling one sideof the spider spring to compress and restore as the plate angulaterelative to one another, while other portions of the spider spring donot.

For example, referring to FIG. 5.2, other spider springs (e.g., spidersprings 200 b 1-b 2, f 1-f 2, j 1-j 2) are designed to have the narrowend of the spider spring rotatably secured to a flat surface on aninwardly facing surface of a plate (e.g., the flat surface 102 a on theinwardly facing surface 104 a of plate 100 a). These spider springspreferably have a central hub (e.g., 204 b 1-b 2, f 1-f 2, j 1-j 2) witha bore (e.g., 206 b 1-b 2, f 1-f 2, j 1-j 2) through which a flangedfastener (e.g., rivet, plug, dowel, or screw; a flanged rivet 115 a isused herein as an example) (shown in FIG. 5.2) can be passed and securedto the flat surface of the plate. The flanged rivet 115 a has a flangedportion at the end of a post portion. The post portion has a diametersmaller than the diameter of the bore, and a length that is longer thanthe thickness of the spider spring's central hub, and the flangedportion has a diameter greater than the diameter of the bore. Therefore,upon application of the rivet 115 a, the spider spring is secured to theplate so that it can still rotate with respect to the plate. (If asimilarly flanged screw is used, a threaded bore can be provided in theplate for its acceptance.) As also discussed below with regard to thesecuring of the wide end of the spider spring, the plates aresecondarily rotatable relative to one another because the wide end ofthe spider spring can rotate with respect to the plate having thecircular recess in which the wide end seats (discussed below). Further,the plates are angulatable relative to one another because the springarms of the spider spring can individually compress and restore,enabling one side of the spider spring to compress and restore as theplates angulate relative to one another, while other portions of thespider spring do not.

For another example, and referring to FIG. 5.3, other spider springs(e.g., spider springs 200 c 1-c 2, g 1-g 2, k 1-k 2) are designed tohave the narrow end cooperate with a semispherical (e.g., ball-shaped)protuberance on an inwardly facing surface of a plate (e.g., theball-shaped protuberance 102 c on the inwardly facing surface 104 c ofplate 100 c). These spider springs preferably have a central hub (e.g.,204 c 1-c 2, g 1-g 2, k 1-k 2) with a curvate socket (e.g., 206 c 1-c 2,g 1-g 2, k 1-k 2) within which the ball-shaped protuberance is securablefor free rotation and angulation through a range of angles. Thestructure of the curvate socket and the coupling of the ball-shapedprotuberance with the curvate socket are described above with regard tothe curvate socket 102 d on plate 100 d and the ball-shaped protuberance102 c on plate 100 c. As noted above, a deflection preventing element(e.g., rivet, plug, dowel, or screw; a rivet 124 c is used herein as anexample) applied to the axial bore 122 c after the ball-shapedprotuberance 102 c has been inserted into the curvate socket preventsthe deflection of the ball-shaped protuberance 102 c so that it does notescape the curvate socket. The plates are rotatable relative to oneanother primarily because the ball-shaped protuberance rotates freelywithin the curvate socket, and secondarily because the wide end of thespider spring can rotate with respect to the plate having the circularrecess in which the wide end seats (discussed below). Also, the platesare angulatable relative to one another primarily because theball-shaped protuberance angulates freely within the curvate socket, andsecondarily because the spring arms of the spider spring canindividually compress and restore, enabling one side of the spiderspring to compress and restore as the plates angulate relative to oneanother, while other portions of the spider spring do not.

For another example, and referring to FIG. 5.4, other spider springs(e.g., 200 d 1-d 2, h 1-h 2, l 1-l 2) are designed to have the narrowend cooperate with a curvate socket on an inwardly facing surface of aplate (e.g., the central curvate socket 102 d on plate 100 d). Thesespider springs preferably have a central hub (e.g., 204 d 1-d 2, h 1-h2, l 1-l 2) with a semispherical (e.g., ball-shaped) protuberance (e.g.,206 d 1-d 2, h 1-h 2, l 1-l 2) that is securable within the curvatesocket for free rotation and angulation through a range of angles. Thestructure of the ball-shaped protuberance and the coupling of theball-shaped protuberance with the curvate socket are as described abovewith regard to the curvate socket 102 d on plate 100 d and theball-shaped protuberance 102 c on plate 100 c. Similar to rivet 124 cdiscussed above, a deflection preventing element (e.g., a rivet, plug,dowel, or screw; rivets 224 d 1-d 2, h 1-h 2, l 1-l 2 are used herein asexamples) applied to the axial bore (e.g., 222 d 1-d 2, h 1-h 2, l 1-l2) after the ball-shaped protuberance (e.g., 206 d 1-d 2, h 1-h 2, l 1-l2) has been inserted into the curvate socket 102 d prevents thedeflection of the ball-shaped protuberance so that it does not escapethe curvate socket. The plates are rotatable relative to one anotherprimarily because the ball-shaped protuberance rotates freely within thecurvate socket, and secondarily because the wide end of the spiderspring can rotate with respect to the plate having the circular recessin which the wide end seats (discussed below). Also, the plates areangulatable relative to one another primarily because the ball-shapedprotuberance angulates freely within the curvate socket, and secondarilybecause the spring arms of the spider spring can individually compressand restore, enabling one side of the spider spring to compress andrestore as the plates angulate relative to one another, while otherportions of the spider spring do not.

For another example, and referring to FIGS. 5.1 through 5.7, each of thespider springs is to have the wide end of the spider spring seat withina circular recess on an inwardly facing surface of a plate (e.g., thecircular recess 102 b on an inwardly facing surface 104 b of plate 100b). More specifically, the wide end of the spider spring (e.g., 200 a1-l 2) fits within the circular recess 102 b with room to expand whenthe spider spring (e.g., 200 a 1-l 2) is under compression. Because thediameter of the circular recess is greater than the diameter of the wideend of the spider spring, unrestrained rotation of the spider springrelative to the plate is enabled, and compressive loading of theartificial disc (and therefore of the spider spring) results in anunrestrained radial deflection of the spider spring, both as necessaryfor proper anatomical response. To prevent removal of the wide end ofthe spider spring from the circular recess when the artificial disc isloaded in tension, a shield 118 b can be placed over the spider springand secured by fasteners (e.g., a rivet, plug, dowel, or screw; rivets116 b are used herein as examples). The shield 118 b can have a centralhole 120 b through which the curvate socket and the ball-shapedprotuberance can pass (where applicable depending on the particularspider spring used) to accommodate efficient assembly of the artificialdisc. The shield 118 b can alternatively or additionally be formed frommultiple shield parts, which would be useful, for example, inembodiments where no part of the spider member can pass through thecentral hole (see, e.g., the embodiment of FIG. 5.4, discussed below).

For another example, and referring to FIG. 5.5, some spider springs(e.g., spider springs 200 a 5-a 6, e 5-e 6, i 5-i 6) are disposablebetween plates having the circular recess (e.g., plates of plateembodiment 100 b), preferably those embodiments in which the spring armsare doubled, with a lower set extending radially downwardly from thecentral hub and an upper set extending radially upwardly from thecentral hub (see, e.g., FIGS. 3.5 and 3.6 for side cross-section viewsof exemplary embodiments) or in which some spring arms extend radiallydownwardly from the central hub and other spring arms extend radiallyupwardly from the central hub (see, e.g., FIGS. 3.3 and 3.4 for sidecross-section views of exemplary embodiments), both in contrast toembodiments in which all of the spring arms extend downwardly or inwhich all of the spring arms extend upwardly (see, e.g., FIGS. 3.1 and3.2 for side cross-section views of exemplary embodiments). These spidersprings have two wide ends, each of which can be retained within acircular recess 102 b of a plate 100 b as shown in FIG. 5.5. The platesare rotatable relative to one another because the wide ends of thespider spring can rotate with respect to the plates having the circularrecess in which the wide ends seat (discussed above). Also, the platesare angulatable relative to one another because the spring arms of thespider spring can individually compress and restore, enabling one sideof the spider spring to compress and restore as the plates angulaterelative to one another, while other portions of the spider spring donot.

For another example, and referring to FIG. 5.6, the spider springs(e.g., spider springs 200 d 1-d 2, h 1-h 2, l 1-l 2) that are designedto have the narrow end, with a ball-shaped protuberance (e.g., 206 d 1-d2, h 1-h 2, l 1-l 2), cooperate with a curvate socket 102 d on aninwardly facing surface of a plate 100 d also can cooperate with thespider springs (e.g., spider springs 200 c 1-c 2, g 1-g 2, k 1-k 2) thatare designed to have the narrow end, with a curvate socket (e.g., 206 c1-c 2, g 1-g 2, k 1-k 2), cooperate with a ball-shaped protuberance 102c on an inwardly facing surface of a plate 100 c so that the ball-shapedprotuberance (e.g., 206 d 1-d 2, h 1-h 2, l 1-l 2) of he one spiderspring (e.g., 200 d 1-d 2, h 1-h 2, l 1-l 2) freely rotates andangulates within the curvate socket (e.g., 206 c 1-c 2, g 1-g 2, k 1-k2) of the other spider spring (200 c 1-c 2, g 1-g 2, k 1-k 2) through arange of angles. The structure of the curvate socket and the ball-shapedprotuberance and the coupling of the ball-shaped protuberance with thecurvate socket is as described above, and the wide ends of thecombination spider spring are retained within a circular recess 102 b ofa respective cooperating plate 100 b as shown in FIG. 5.6. The platesare rotatable relative to one another primarily because the ball-shapedprotuberance rotates freely within the curvate socket, and secondarilybecause the wide ends of the spider springs can rotate with respect tothe plates having the circular recesses in which the wide ends seat(discussed above). Also, the plates are angulatable relative to oneanother primarily because the ball-shaped protuberance angulates freelywithin the curvate socket, and secondarily because the spring arms ofthe spider springs can individually compress and restore, enabling oneside of each spider spring to compress and restore as the platesangulate relative to one another, while other portions of the spiderspring do not.

For another example, referring to FIG. 5.7, similar to FIG. 5.2, inwhich a spider spring having a bored central hub (e.g., spider springs200 b 1-b 2, f 1-f 2, j 1-j 2) is rotatably secured to a flat surface onan inwardly facing surface of a plate by a flanged fastener (e.g.,rivet, plug, dowel, or screw; rivet 115 a is used herein as an example),the same type of spider spring can be rotatably secured to a narrow endof an opposing spider spring, the narrow end of the opposing spiderspring having a flanged post. The flanged post, similar to the flangedrivet 115 a of FIG. 5.2, has a flanged portion at the end of a postportion. The post portion has a diameter smaller than the diameter ofthe bore, and a length that is longer than the thickness of the boredspider spring's central hub, and the flanged portion has a diametergreater than the diameter of the bore. Thus, when the spider springs arecoupled at their narrow ends so that the post portion passes through thebore and the flanged portion maintains the narrow end of the boredspider spring adjacent the narrow end of the opposing spider spring, thenarrow ends are secured to one another so that they can still rotatewith respect to one another. While any type of flanged post can be usedwithin the scope of the invention, including but not limited to athreaded flanged post cooperating with a threaded bore at the narrow endof the opposing spider spring, FIG. 5.7 illustrates as one example aspider spring having a bored central hub (e.g., spider springs 200 b 1-b2, f 1-f 2, j 1-j 2) being rotatably secured in this fashion to a spiderspring having a ball-shaped protuberance on its narrow end (e.g., spidersprings 200 d 1-d 2, h 1-h 2, l 1-l 2), wherein the ball-shapedprotuberance (e.g., 206 d 1-d 2, h 1-h 2, l 1-l 2) functions as thediscussed flanged post. As noted above, the ball-shaped protuberance canradially compress to fit through the bore (e.g., 200 b 1-b 2, f 1-f 2, j1-j 2) to couple the spider springs to one another, and then adeflection preventing element (e.g., rivet, plug, dowel, or screw;rivets 224 d 1-d 2, h 1-h 2, l 1-l 2 are used herein as examples) can beapplied to the axial bore (e.g., 222 d 1-d 2, h 1-h 2, l 1-l 2) of theball-shaped protuberance to prevent the ball-shaped protuberance fromthereafter radially compressing so that it cannot pass through the bore(e.g., 206 b 1-b 2, f 1-f 2, j 1-j 2) again. The plates are rotatablerelative to one another primarily because the coupling enable the narrowends of the spider springs to rotate relative to one another, andsecondarily because the wide ends of the spider springs can rotate withrespect to the plates having the circular recess in which the wide endsseat (discussed above). Also, the plates are angulatable relative to oneanother primarily because the spring arms of the spider springs canindividually compress and restore, enabling one side of each spiderspring to compress and restore as the plates angulate relative to oneanother, while other portions of the spider spring do not.

For another example, and referring to FIG. 5.8, some embodiments of theartificial disc of the invention can forgo a spider spring altogether ifaxial compressibility is not desirable in a particular clinicalapplication. More specifically, plates having a ball-shaped protuberance(e.g., plate of plate embodiment 100 c) can cooperate with plates havinga curvate socket (e.g., plates of plate embodiment 100 d) so that theball-shaped protuberance 102 c of the one plate 100 c freely rotates andangulates within the curvate socket and the ball-shaped protuberance andthe coupling of the ball-shaped protuberance with the curvate socket isas described above. The plates are rotatable relative to one anotherbecause the ball-shaped protuberance rotates freely within the curvatesocket, and angulatable relative to one another because the ball-shapedprotuberance angulates freely within the curvate socket.

The embodiments having a ball-and-socket joint as described above,because the ball-shaped protuberance is held within the curvate socketby a rivet in the axial bore preventing radial compression of theball-shaped protuberance, the artificial disc can withstand tensionloading of the plates, as necessary for proper anatomical response. Moreparticularly, when a tension load is applied to the plates, theball-shaped protuberance in the curvate socket seeks to radiallycompress to fit through the opening of the curvate socket. However, therivet in the axial bore of the ball-shaped protuberance prevents theradial compression, thereby preventing the ball-shaped protuberance fromexiting the curvate socket. Further, in embodiments that have(additionally or alternatively) a spider spring, as the wide end of thespider spring seeks to escape the circular recess of the plate, therivets holding the shield in place over the spider spring prevent theshield from separating from the plate when the spider spring pressesagainst the inner surface of the shield. Further, in embodiments wherethe narrow end of the spider spring is secured against a plate or anarrow end of another spider spring by a rivet, rotatably or otherwise,the flanged portion of the rivet prevents the separation of the narrowend(s) of the spider spring(s). Therefore, the assembly does not comeapart under normally experienced tension loads. This ensures that noindividual parts of the assembly will pop out or slip out from betweenthe vertebral bodies when the patient stretches or hangs whileexercising or performing other activities. Thus, in combination with thesecuring of the plates to the adjacent vertebral bones via the meshdomes, the disc assembly has an integrity similar to the tension-bearingintegrity of a healthy natural intervertebral disc.

Further, because the plates in some embodiments are made angulatablerelative to one another by the ball-shaped protuberance being rotatablyand angulatably coupled in a curvate socket, the disc assembly providesa centroid of motion within the ball-shaped protuberance. Accordingly,in those embodiments, the centroid of motion of the disc assemblyremains centrally located between the vertebral bodies, similar to thecentroid of motion in a health natural intervertebral disc.

While there has been described and illustrated specific embodiments ofan artificial disc, it will be apparent to those skilled in the art thatvariations and modifications are possible without deviating from thebroad spirit and principle of the invention. The invention, therefore,shall not be limited to the specific embodiments discussed herein.

1. An intervertebral implant comprising: a first plate having an innersurface, an outer surface, a ball shaped protuberance projecting fromthe inner surface and an annular groove surrounding the ball shapedprotuberance; a second plate having an inner surface, an outer surface,a curvate socket formed in the inner surface of said second plate and araised rim surrounding the curvate socket; said first and second platesbeing assembled together so that the inner surfaces of said platesoppose one another and with the ball shaped protuberance disposed in thecurvate socket and the annular groove aligned with the raised rim,wherein the assembled first and second plates angulate and rotaterelative to one another.
 2. The implant as claimed in claim 1, whereinthe ball shaped protuberance is inwardly deflectable.
 3. The implant asclaimed in claim 2, wherein the ball shaped protuberance has a firstradius in an undeflected state and a smaller second radius in adeflected state.
 4. The implant as claimed in claim 3, wherein thecurvate socket of said second plate has a radius that is smaller thanthe first radius of the ball shaped protuberance when the ball shapedprotuberance is in the undeflected state.
 5. The implant as claimed inclaim 2, wherein the ball shaped protuberance has an axial bore formedtherein and the device further comprises a deflection preventing elementinsertible into the axial bore.
 6. The implant as claimed in claim 5,wherein the deflection preventing element is selected from the groupconsisting of a rivet, a plug, a dowel and a screw.
 7. The implant asclaimed in claim 5, wherein said second plate has an opening formedtherein and the deflection preventing element is passable through theopening in said second plate.
 8. The implant as claimed in claim 1,wherein the ball shaped protuberance is centrally located on said firstplate and the curvate socket is centrally located on said second plate.9. The implant as claimed in claim 1, wherein the inner surface of saidsecond plate has a region outside the raised rim that slopes toward theouter surface of said second plate.
 10. The implant as claimed in claim1, further comprising a mesh overlying the outer surface of one of saidfirst and second plates.
 11. The implant as claimed 10, wherein theouter surface of the one of said first and second plates has a recessand the mesh overlies the recess.
 12. The implant as claimed in claim 1,wherein the raised rim of said second plate advances into the annulargroove of said first plate when said first and second plates are angledrelative to one another.
 13. The implant as claimed in claim 1, theinner surface of said first plate having a central region and aperipheral region outside the central region that slopes toward theouter surface of said first plate.
 14. An intervertebral implantcomprising: a first plate having an inner surface, an outer surface, aninwardly deflectable ball shaped protuberance projecting from the innersurface and an annular groove surrounding the ball shaped protuberance;a second plate having an inner surface, an outer surface, a curvatesocket formed in the inner surface of said second plate and a raised rimsurrounding the curvate socket; said first and second plates beingassembled together so that the inner surfaces of said plates oppose oneanother and the inwardly deflectable ball shaped protuberance isdisposed in the curvate socket, wherein the annular groove on said firstplate is aligned with the raised rim on said second plate, the raisedrim advancing into the annular groove when said first and second platesare angled relative to one another.
 15. The implant as claimed in claim14, wherein the ball shaped protuberance is integrally formed with saidfirst plate and the curvate socket is integrally formed with said secondplate.
 16. The implant as claimed in claim 14, further comprising adeflection preventing element inserted in an axial bore of said ballshaped protuberance for preventing inward deflection of said ball shapedprotuberance.
 17. An intervertebral implant comprising: a first platehaving an inner surface, an outer surface, a ball shaped protuberanceintegrally formed with said first plate and projecting from the innersurface and an annular groove formed in the inner surface of said firstplate and surrounding the ball shaped protuberance; a second platehaving an inner surface, an outer surface, a curvate socket integrallyformed with said second plate and provided in the inner surface of saidsecond plate and a raised rim surrounding the curvate socket; said firstand second plates being assembled together with the ball shapedprotuberance inserted in the curvate socket, wherein the raised rim onsaid second plate advances into the annular groove on said first platefor increasing a range of angulation of the said first and second platesrelative to one another.
 18. The implant as claimed in claim 17, whereinthe ball shaped protuberance is inwardly deflectable for being insertedinto the curvate socket, the ball shaped protuberance having an axialbore for receiving a deflection preventing element that prevents inwarddeflection of the ball shaped protuberance after the ball shapedprotuberance has been received in the curvate socket of said secondplate.
 19. The implant as claimed in claim 17, wherein the inner surfaceof said first plate opposes the inner surface of said second plate, theopposing inner surfaces sloping away from one another for increasing arange of angulation of the said first and second plates relative to oneanother.
 20. The implant as claimed in claim 17, further comprising amesh overlying at least one of the outer surfaces of said first andsecond plates.